Jag/automount

.gitignore

@@ -0,0 +1,2 @@
+.clang-format
+.nvimrc

Makefile

@@ -7,3 +7,4 @@ ifndef SHELLCHECK
 endif
 	shellcheck -a -x \
 		vmctl cmd/* common/* lib/qemu/*
+

README.md

@@ -129,6 +129,37 @@ add the following text to your configruation file (usually /etc/nix/nix.conf):
     experimental-features = nix-command flakes
 
 
+### Mounting directories
+
+This is useful when selftests or modules are needed within the VM.
+
+1. Early mount: Add a `qemu_share_add` to your vmctl config
+
+    ```sh
+      qemu_share_add \
+        --shared-dir "/path/to/modules/lib/modules" \
+        --tag "modules" \
+        --share-type "virtiofs" \
+        --vm-dir "/lib/modules"
+    ```
+
+    If you want to share but not mount, remove the --vm-dir arg.
+
+2. Systemd mount: Add a "service" to your nix configuration:
+
+    ```nix
+        systemd.services.mount-user-virtiofs = {
+          description = "Mount virtiofsd tag 'selftests' to /usr/lib/kselftests";
+          after = [ "local-fs.target" ];
+          wantedBy = [ "multi-user.target" ];
+          serviceConfig = {
+            Type = "oneshot";
+            ExecStart = "/run/current-system/sw/bin/mount -t virtiofs user /usr/lib/kselftests";
+            RemainAfterExit = true;
+          };
+        };
+    ```
+
 ## Prep boot img
 
 The base configruation `*-base.conf` will look for a base image in

contrib/nix/vmctl_init.c

@@ -1,8 +1,10 @@
+#include "limits.h"
 #include <unistd.h>
 #include <sys/mount.h>
 #include <sys/stat.h>
 #include <errno.h>
 #include <string.h>
+#include <stdlib.h>
 
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 
@@ -11,97 +13,168 @@
 #include <stdio.h>
 #include <stdarg.h>
 
-char const * const indent_str = "    ";
-static void info(unsigned indent, char const *fmt, ...) {
-    while(0 != indent--)
-        fprintf(stdout, "%s", indent_str);
+char const *const indent_str = "    ";
+static void info(unsigned indent, char const *fmt, ...)
+{
+	while (0 != indent--)
+		fprintf(stdout, "%s", indent_str);
 
-    va_list args;
-    va_start(args, fmt);
-    vfprintf(stdout, fmt, args);
-    va_end(args);
+	va_list args;
+	va_start(args, fmt);
+	vfprintf(stdout, fmt, args);
+	va_end(args);
 
-    fprintf(stdout, "\n");
+	fprintf(stdout, "\n");
 }
-static void prnt_args(int argc, char *argv[]) {
-    info(1, "Arguments :\n");
-    info(2, "argc = %d\n", argc);
-    info(2, "argv:\n");
-    for (int i = 0; i < argc; i++)
-        info(3, "argv[%d] = %s\n", i, argv[i]);
+static void prnt_args(int argc, char *argv[])
+{
+	info(1, "VMCTL image-less INIT started ... \n");
+	info(1, "Arguments :\n");
+	info(2, "argc = %d\n", argc);
+	info(2, "argv:\n");
+	for (int i = 0; i < argc; i++)
+		info(3, "argv[%d] = %s\n", i, argv[i]);
 }
 
 #else
-static inline void info(unsigned indent, char const *fmt, ...) {}
-static inline void prnt_args(int argc, char *argv[]) {}
+static inline void info(unsigned indent, char const *fmt, ...)
+{
+}
+static inline void prnt_args(int argc, char *argv[])
+{
+}
 #endif
 
 struct ArgOpt{
-    const char *arg_str;
-    char **arg_val;
+	const char *arg_str;
+	char ***arg_vals;
+	int *count;
 };
 
-void parse_args(int const argc, char *argv[], struct ArgOpt *opts, int const opts_count) {
-    for (int i = 1; i < argc; i++) {
-        for (int j = 0; j < opts_count; j++) {
-            if (strcmp(argv[i], opts[j].arg_str) == 0 && i + 1 < argc) {
-                *opts[j].arg_val = argv[i + 1];
-                i++;
-                break;
-            }
-        }
-    }
+// Parse function to match arguments and store their values
+void parse_args(int argc, char *argv[], struct ArgOpt *options, int option_count) {
+	for (int i = 1; i < argc; i++) {
+		for (int j = 0; j < option_count; j++) {
+			if (strcmp(argv[i], options[j].arg_str) == 0 && i + 1 < argc) {
+				(*options[j].count)++;
+				*options[j].arg_vals =
+					realloc(*options[j].arg_vals,
+						(*options[j].count) * sizeof(char *));
+				(*options[j].arg_vals)[(*options[j].count) - 1] = argv[i + 1];
+				i++;
+				break;
+			}
+		}
+	}
 }
 
-int ensure_dir(const char *path) {
-    if (mkdir(path, 0755) == -1 && errno != EEXIST) {
-        info(1, "Error: creating the path (%s)", path);
-        return -1;
-    }
-    return 0;
-}
+int ensure_dir(char *path)
+{
+	if (path[0] == '\0')
+		return -1;
 
-int mount_nix_store() {
-    int ret;
-    // This must match the tag used in virtiofsd
-    const char *source = "nixstore";
-    const char *target = "/nix/store";
+	for(int idx = 1, path_end =0; idx < PATH_MAX; ++idx) {
+		if (path[idx] != '/' && path[idx] != '\0')
+			continue;
 
-    if (ensure_dir("/nix") || ensure_dir("/nix/store"))
-        return 1;
+		if (path[idx] == '\0')
+			path_end = 1;
+		else
+			path[idx] = '\0';
 
-    if (mount(source, target, "virtiofs", 0, "") == -1) {
-        info(1, "Error: mounting source (%s) at target (%s)", source, target);
-        return 1;
-    }
+		if (mkdir(path, 0755) == -1 && errno != EEXIST)
+			goto err;
 
-    info(1, "Mounted %s at %s\n", source, target);
+		if (path_end)
+			return 0;
+		else
+			path[idx] = '/';
+	}
+
+err:
+	info(1, "Error: creating the path (%s)", path);
+	return -1;
+
+}
 
-    return 0;
+int read_until(const char *str, char c)
+{
+	int idx;
+	for(idx = 0 ; str[idx] != '\0' && str[idx] != c; ++idx)
+		;
+	return idx;
 }
 
-int main(int argc, char *argv[]) {
-    int ret;
-    char *init_path = NULL;
-    struct ArgOpt opts[] = {
-        {"--init-path",  &init_path},
-    };
+/* mount_str: mount str (SHARE_NAME;MOUNT_PATH;MOUNT_TYPE) */
+int mount_from_str(char *mount_str)
+{
+	int idx, i = 0, end = 0;
+	char *strs[3] = {mount_str, NULL, NULL};
 
-    info(1, "VMCTL image-less INIT started ... \n");
-    prnt_args(argc, argv);
+	info(1, "Mount string: %s", mount_str);
+	do {
+		idx = read_until(strs[i], ',');
+		if (idx == 0)
+			break;
 
-    parse_args(argc, argv, opts, ARRAY_SIZE(opts));
-    if (init_path == NULL) {
-      info(1, "Error: missing --init-path arg\n");
-      return -1;
-    }
+		if(strs[i][idx] == '\0')
+			end = 1;
+		else {
+			strs[i][idx] = '\0';
+			strs[i+1] = strs[i] + idx + 1;
+		}
 
-    if(mount_nix_store())
-      return 1;
+		if (end)
+			break;
 
-    info(1, "Attempting to exec: %s\n", init_path);
-    execv(init_path, argv);
-    info(1, "Error: execv failed");
+		i++;
+	} while (i < 3);
+
+	if (strs[1] == NULL || strs[2] == NULL)
+		return -1;
+
+	if (ensure_dir(strs[1]))
+		return -1;
+
+	if (mount(strs[0], strs[1], strs[2], 0, "") == -1) {
+		info(1, "Error: mounting %s at %s. errno %d",
+		     strs[0], strs[1], errno);
+		return 1;
+	}
+
+	info(1, "Mounted %s at %s\n", strs[0], strs[1]);
+
+	return 0;
+}
 
-    return -1;
+int main(int argc, char *argv[])
+{
+	int ret;
+	char **mount_strs = NULL, **init_paths = NULL;
+	int mounts_count = 0, init_paths_count = 0;
+	struct ArgOpt opts[] = {
+		{"--init-path", &init_paths, &init_paths_count},
+		{"--mount", &mount_strs, &mounts_count},
+	};
+
+	prnt_args(argc, argv);
+	parse_args(argc, argv, opts, ARRAY_SIZE(opts));
+	if (init_paths_count != 1) {
+		info(1, "Error: %s --init-path arg",
+		     init_paths_count == 0 ? "missing" : "too many");
+		return -1;
+	}
+
+	for (int i = 0; i < mounts_count; ++i) {
+		if (mount_from_str(mount_strs[i])) {
+			info(1, "Error: Could not mount");
+			return -1;
+		}
+	}
+
+	info(1, "Attempting to exec: %s\n", init_paths[0]);
+	execv(init_paths[0], argv);
+	info(1, "Error: execv failed");
+
+	return -1;
 }

lib/qemu/nix

@@ -103,19 +103,27 @@ qemu_nix_add_noimgnix () {
 
   _qemu_nix_create_nix_init "${VMSTATE}"
 
+  qemu_share_add --shared-dir "${NIX_STORE_PATH}" \
+      --tag "nixstore" \
+      --share-type "virtiofs" \
+      --vm-dir "/nix/store"
+
   local nix_init_path=""
   nix_init_path="$(readlink "${dst_path}")/init"
   local cmd_line="root=/dev/ram0 console=${GUEST_KERNEL_CONSOLE}"
   if [[ -v GUEST_KERNEL_APPEND_EXTRA ]]; then
     cmd_line="${cmd_line} ${GUEST_KERNEL_APPEND_EXTRA}"
   fi
-  cmd_line="${cmd_line} ${cmd_line_extra} -- --init-path ${nix_init_path}"
+  cmd_line="${cmd_line} ${cmd_line_extra}"
+  cmd_line="${cmd_line} -- --init-path ${nix_init_path}"
+  if [[ -v NIX_MOUNTS ]]; then
+    for nmount in "${NIX_MOUNTS[@]}"; do
+      cmd_line="${cmd_line} --mount ${nmount}"
+    done
+  fi
 
   QEMU_PARAMS+=("-kernel" "${kernel_dir}/${GUEST_KERNEL_IMAGE}")
   QEMU_PARAMS+=("-append" "${cmd_line}")
   QEMU_PARAMS+=("-initrd" "${VMSTATE}/init.img")
 
-  qemu_share_add --shared-dir "${NIX_STORE_PATH}" \
-      --tag "nixstore" \
-      --share-type "viofs"
 }

lib/qemu/share

@@ -43,7 +43,7 @@ qemu_share_add_9p() {
 }
 
 qemu_share_add() {
-  local long="shared-dir:,tag:,share-type:"
+  local long="shared-dir:,tag:,share-type:,vm-dir:"
 
   if ! tmp=$(getopt -o "" --long "$long" -n "${FUNCNAME[0]}" -- "$@"); then
     exit 1
@@ -63,6 +63,9 @@ qemu_share_add() {
       '--tag' )
         local tag="$2"; shift 2;
         ;;
+      '--vm-dir' )
+        local vm_dir="$2"; shift 2;
+        ;;
       '--' )
         shift; break
         ;;
@@ -90,10 +93,17 @@ qemu_share_add() {
 
   if [[ "${share_type}" == "9p" ]]; then
     qemu_share_add_9p "${shared_dir}" "${tag}"
-  elif [[ "${share_type}" == "viofs" ]]; then
+  elif [[ "${share_type}" == "virtiofs" ]]; then
     qemu_share_add_virtiofsd "${shared_dir}" "${tag}"
   else
     _fatal 1 "${FUNCNAME[0]}: Unknown directory share type (${share_type})"
   fi
+
+  if [[ -v vm_dir ]]; then
+    if [[ ! -v NIX_STORE_PATH ]]; then
+      _log "vm-dir ignored! it's only active in NIX"
+    fi
+    NIX_MOUNTS+=("${tag},${vm_dir},${share_type}")
+  fi
 }